Strainer (1) for fibrous suspensions, comprising a container (2), a filtering basket (3; 21, 22) inside the container (2) and a rotor (4; 15, 16) inside the filtering basket (3; 21, 22) coupled to motorization means (7) suited to set it rotating. In the container (2) there are a drain chamber (35) of the rejected suspension, a delivery chamber (25, 27) of the filtered suspension, and a collector body (30) arranged in the upper part of the container (2). The collector body (30) comprises a lower collector (37) and an upper collector (38), both with radial longitudinal profile in the shape of a truncated cone and connected to each other in correspondence with the long bases (37a, 38a). The lower collector (37) has its short base (37b) facing the filtering basket (3; 21, 22) and the upper collector (38) has its short base (38b) facing upwards.